The metro buses I ride in to St. Louis do not have seat belts, do not have soft seats, and are not high but they drive on the freeway at 65+ MPH. It's even legit just to stand which I've done when the bus is crowded. None of this has ever felt safe to me but I assumed someone had determined that it was. For instance, I had not known how effective school busses' high, padded seats were at protecting its passengers until reading this thread and had assumed similarly that they didn't seem safe but must be.